The present invention relates generally to a monitoring system adapted to detect the presence of an insult in an absorbent article while it is being worn by a wearer. More particularly, the present invention relates to wetness monitors and wetness monitoring methods that reduce the amount and/or rate of corrosion of the conductors located within the absorbent articles.
Disposable absorbent articles find widespread use as personal care products such as diapers, children's toilet training pants and other infant and child care products, adult incontinence garments and other adult care products, sanitary napkins and other feminine care products, and the like, as well as surgical bandages and sponges and medical garments. These articles absorb and contain body waste and are intended to be discarded after a limited period of use; i.e., the articles are not intended to be laundered or otherwise restored for reuse. Conventional disposable absorbent articles include an absorbent body disposed between an inner layer adapted for contacting the wearer's skin and an outer layer for inhibiting liquid waste absorbed by the absorbent body from leaking out of the article. The inner layer of the absorbent article is typically liquid permeable to permit body waste to pass through for absorption by the absorbent body.
Disposable absorbent training pants, in particular, are useful in toilet training children. Typically, these disposable undergarments are similar to washable, cloth underwear in the manner in which they are put on and worn, yet provide an absorbent function similar to diapers to maintain skin health. Training pants provide a child undergoing toilet training with an undergarment that eases the transition from diapers to washable, cloth underwear as they become more confident in their ability to use the toilet independently.
Monitoring of a toilet-training child by a caregiver can be helpful in that when urination occurs it can be discussed by the child and caregiver to enhance and improve the learning experience. Therefore, it is beneficial to provide the caregiver with immediate notification and/or verification that urination has occurred so that it may be discussed with the child while the event is still fresh in the child's mind.
Likewise, caregivers tending to the hygienic needs of care recipients can benefit by monitoring the occurrences of urination in the care recipients so that the absorbent articles may be changed when necessary, but repeated inspection is not required. Therefore, it is beneficial to provide the caregiver with immediate notification that urination has occurred so that appropriate action may be taken.
One way of monitoring urination is by using a system that detects a change in an electrical property of the undergarment wherein the electrical property is a function of the wetness of the undergarment. For example, the electrical property may be resistance, conductance, impedance, capacitance or any other parameter which varies as the wetness of the undergarment varies. For example, a pair of spaced apart parallel conductors may be situated within or proximate the absorbent material of the undergarment. These conductors may be in electrical contact with the absorbent material of the undergarment and may be connected to a monitor to complete a wetness circuit including a power source, such as a battery. For example, the circuit may include a voltage divider for detecting resistance between the conductors.
The output of the circuit may be an analog output voltage that corresponds to a resistance value. When the undergarment is dry, the resistance between the conductors is expected to be extremely high and relatively infinite, appearing as an open circuit. When the undergarment is wet, more particularly when the absorbent material of the undergarment between the conductors becomes wet, the resistance of the undergarment at that area is expected to drop to a relatively lower value because urine acts as a conductor.
Accordingly, in a conventional system the resistance between the conductors is monitored and compared to a predetermined and fixed threshold resistance value. If a resistance value is less than the threshold resistance value, then the wetness circuit sends a signal to an indicator, which notifies the caregiver and/or the wearer that the wearer has urinated.
As noted above, these articles are intended to be discarded after a limited period of use. As such, the conductors are desirably thin foil strips or the like. For example, the conductors may be vapor deposited films because they can be economically produced. However, vapor deposited foils are susceptible to corrosion by electrochemical reaction which can result in electrical performance loss. Once urine insults the product, aluminum ions from the conductors are removed and put in mobile phase across the potential of the open electronic circuit. Within a short amount of time, the foils lose electrical continuity along the length of the product making wetness detection difficult or inaccurate.
Several parameters influence this electrochemical reaction. First, aluminum is a very reactive metal within electrochemical cells and the ions of the urine are a perfect electrochemical solution to encourage the active transfer of the metal ions from the conductor to the mobile phase. Second, even a small potential difference applied across the conductors can have significant effect on the duration of the conductors' continuity. Finally, in near-body sensor systems, like those discussed herein, DC power is preferable because it is simple, it satisfies the power needs, and it is safe. However, DC power has been found to greatly accelerate the corrosion of the conductors.
Thus, despite their usefulness, conventional devices may be prone to corrosion by electrochemical reaction. Accordingly, there is a need for wetness monitoring systems that provide wetness notification and a method of reducing sensor corrosion.